Tube cleaner

ABSTRACT

The invention is concerned with a device for the internal cleaning, under operation, of the tubes of a heat exchanger containing a plurality of substantially straight tubes (1a,1b,1c) having both ends fastened to tube sheets (2), head chambers outside the tube sheets for the medium flowing through the tubes, cleaning members (26,30) in the tubes, and driving means comprising cables (27,31) and cable drums (13,14) to propel the cleaning members forward and backward in the tubes. The cleaning device is characterized in that the cleaning member is a helical spring (26,30) and that the cables (27,31) are endless cables, or cables having a limited length, which extend over the cable drums (13,14) in the head chambers (11,12).

FIELD OF THE INVENTION

The invention relates to a device for the internal cleaning, underoperation, of the tubes of a heat exchanger containing a plurality ofsubstantially straight tubes, a shell surrounding said tubes, and headchambers at the ends of the heat exchanger. The number of tubes may varyfrom a few to thousands of tubes. The heat exchanger is part ofequipment, and it may be built into said equipment, or it may becombined with said equipment, or it may stand separate from saidequipment. In the first two types of heat exchanger the shell or thehead chambers may be parts of the equipment. The heat exchanger may bemounted in a horizontal or vertical position.

PRIOR ART

The nominal effect of a heat exchanger is based on the assumption thatthe heat transfer from the tube wall to the medium inside the tube, orthe reverse, is not deteriorated by any coating which insulates andwhich reduces the flow velocity in the tube. Such a coating occurs,however, in most processes. It is very inconvenient, particularly incontinuous processes, to have to reckon with a sinking effect of theheat exchangers. In addition, such a coating may stop the production,and may deteriorate the yield by changing the ratio of the desired tothe undesired product. It may also increase the consumption of steam.

Such a coating on the tube wall may be of various types. In heatexchangers for a comparatively low temperature, for example inwaterworks and sewage treating plants, the coating may consist of softsludge. In heat exchangers for a comparatively high temperature, forexample in chemical and petrochemical processing industries, the coatingmay consist of viscous tar, coke, and soot. In other heat exchangers,for example in the cellulose processing industry, the coating may formbrittle deposits.

Few heat exchangers have means for the internal cleaning of the tubesunder operation. The majority of heat exchangers are cleaned afterhaving been taken apart during a stop of operation. Heat exchangers areoften made oversize, to prolong the interval between cleaningoperations. A cleaned heat exchanger is often kept in reserve, tominimize the time for the stop of operation. Such measures, however,necessitate an increased investment. Generally, the cost for cleaningthe tubes and associated operations during the lifetime of a heatexchanger, say 5 years, correspond to 3 times the investment for theheat exchanger. To said cost must be added the costs for theinterruptions of operation, the reduced production, and the lower yield,said additional costs being often considerable. The cleaning of thetubes after discontinuing the operation and taking the heat exchangerapart is considered to be one of the dirtiest industrial jobs.

Several methods have been suggested for cleaning the tubes underoperation. In one known method cleaning pistons are moved forward andbackward through the tubes by means of rods, a common driving plate, anda pressurized cylinder. It is an inconvenience of said method that theloss of pressure is comparatively large, and that there is a risk ofdeposition on the cleaning pistons because they have a large surface incontact with the tube wall. It is another inconvenience that the devicerequires a large space, and that it can be used only for heat exchangerscontaining short tubes.

According to the Swedish Pat. No. 317,394 loose brushes are driven bythe pumped medium forward and backward through the tubes. A catchingbasket for the brush is placed at each end of the tube. It is aninconvenience that the medium has to be pumped, that a system of valvesand shunt conduits has to be arranged to reverse the flow of the medium,that a comparatively large loss of pressure is caused by the catchingbasket just outside the tube ends and by the brush inside said catchingbasket, that the mounting of the catching basket requires a deformationof the valuerable tube end, and that the plastic parts and the brushlimit the use of the device to heat exchangers operating mainly withwater and aqueous solutions having a comparatively low temperature andproducing a deposit of soft sludge.

According to U.S. Pat. No. 1,795,348 cleaning balls are propelledcontinuously through the tube by the flowing medium. The balls aresubsequently separated from the medium, and are returned to the inletend of the heat exchanger by a pumped partial flow of the medium. It isan inconvenience that the cleaning is not very good on tough coatings,that balls stay in cavities in the apparatus, and that the balls arestrongly abrasive on the pump and other parts of the apparatus whichchange the direction of the flow.

THE INVENTION

The invention aims at providing an improved cleaning device whichresults in a low flow resistance in the tubes, and which does not sufferfrom the inconveniences mentioned above. The invention is concerned witha cleaning device for the internal cleaning, under operation, of thetubes of a heat exchanger containing a plurality of substantiallystraight tubes having both ends fastened to tube sheets, head chambersoutside the tubes for the medium flowing through the tubes, cleaningmembers in the tubes, and driving means comprising cables and cabledrums to propel the cleaning members forward and backward in the tubes.The cleaning device is characterized in that the cleaning member is ahelical spring, and that the cables are endless cables or cables oflimited length which extend over the cable drums in the head chambers.

A cleaning spring may be fastened to two cables having well definedlengths, one cable being wound upon a cable drum in one of the headchambers while the other cable is being unwound from a cable drum in theother head chamber. It is an inconvenience that this device requires alarge space, and that the tension in the cables will not be welldefined. Therefore, we prefer to use endless cables. An endless cable,as referred to in the specification and claims, shall be interpreted tomean a cable plus one or two cleaning springs.

The cleaning spring is preferably a cylindrical helical spring havingpreferably 11/4-7 turns. In one or both ends the spring may be shapedlike a conical spring. The outer diameter of the spring is preferably alittle smaller than the inner diameter of the tube. A spring of thissize can be brought into scraping contact with the tube wall by thecable being fastened to the spring in a more or less eccentric position,as will be disclosed below. Alternatively, the cleaning spring may have,in its unloaded condition, an outer diameter equal to the inner diameterof the tube, or even a bit larger. In this case it is necessary, duringa running-in period, to apply an increased force of tension to thecable, in order to be able to pull the cleaning spring through the tube.The friction against the tube wall reduces the diameter of the spring.Therefore, after the running-in period only the normal force of tensionis required.

DESCRIPTION OF A PREFERRED EMBODIMENT WITH REFERENCE TO THE DRAWINGS

FIG. 1 is a perspective view of a heat exchanger of the type concerned,involving the invention.

FIGS. 2 and 3 are cross-sections of, in principle, the heat exchanger ofFIG. 1.

FIG. 4 is a top view of the heat exchanger illustrating the pattern ofthe tubes and the positions of the cable drums.

FIG. 5 illustrates a normal endless cable with two cleaning springs.

FIG. 6 illustrates an endless cable having no aligning tube.

FIG. 7 illustrates a cross-section of a member for tightening thecables.

FIG. 8 illustrates a normal cleaning spring.

FIG. 9 is a top view of the spring of FIG. 8.

FIG. 10 is a section of a cable drum having a V-shaped groove containinga cable.

FIG. 11 illustrates a normal cleaning spring, placed inside a tube.

FIG. 12 illustrates a cleaning spring containing the double number ofturns.

FIG. 13 illustrates a connecting member.

FIG. 14 illustrates a cable guide.

FIG. 15 is a perspective view of a section of a stop rod.

The heat exchanger contains a cluster of 355 tubes 1 having a total heattransferring surface of 54 m². The tubes are arranged in a standardizedsymmetric linear pattern, and are fastened at both ends to tube sheets 2which are fastened to a shell 3. The shell is provided with an expansionbellows 4, an inlet 5 for steam, an outlet 6 for condensate, and twosupports 7 for mounting the heat exchanger in upright position. At eachtube sheet 2 there is usually arranged a conical chamber having a flange8 facing the tube sheet 2 and flanges 9, 10 facing the equipment towhich the heat exchanger belongs.

The head chambers consist of an upper housing 11 and a lower housing 12for the cable drums. Each housing 11, 12 contains six cable drums 13, 14having both ends mounted in bearings 15, The upper bearings areimmovably mounted in the upper housing 11, whereas the lower bearings 15are mounted in a movable frame 16. Said frame 16 is suspended from fourtightening members 17 situated above the corners of the lower housing 12and extending down into said housing 12. Each cable drum 13 in the upperhousing 11 has its shaft extending through the bearing 15. A cog wheel18 is mounted on said extended shaft, and said cog wheel engages acorresponding cog wheel 18 on the adjacent cable drum 13. A bracket 19,fastened to the upper housing 11, supports a motor 20 and a gear. Themotor 20 is, via a coupling 21, a shaft 22, and a packing box 62,connected to the cog wheel 18 of one of the two middle cable drums 13.Each cable drum 13, 14 is, according to FIG. 4, designed to serve fourrows of tubes 1, and cooperates with two cable guides 23 which areparallel with the cable drum 13, 14. The cable guides 23 consist of arod having a circular cross section. Each cable guide is mounted on asupport rod 24 which is fastened to the members carrying the bearings 15in the upper housing 11 and in the frame 16 in the lower housing 12. Thesupport rods 24 in the upper housing 11 are fastened to a T-shaped rod24, 25, see FIG. 15, which is provided with open slots 58 at both edges.The number of slots 58 corresponds to the number of cables 27 on thecable drum 13, The slot 58 is wider than the diameter of the cable 27but narrower than the diameter of the wire forming the cleaning spring26.

The cable guides 23 consist of round rods of hardened steel. They arefastened by screws to supporting flat rods 24, 25. The diameter of theround rod corresponds to the distance between the cables 27, 28 of twoadjacent rows of tubes 1. The thickness of the supporting rod 24 issmaller than the diameter of the round iron 23. The cable guide 23directs the cable 27, 28 to go clear from the edge of the tube 1, so asto prevent the cable from wearing grooves into the edge of the tube. Allcables 27, 28 between the cable drums 13, 14 and the tubes extend on thesame side of the cable guide 23. Consequently, the length of contactbetween the cables 27, 28 and the V-shaped grooves 29 in the cable drumwill be equal for all cables, and the pulling effect of the cable drumon the cables will be equal. The cable guides 23 can be omitted if theslots 58 have rounded bottom surfaces, so that the cables can slide onsaid surfaces without wear. In this case the rods 25 preferably consistof hardened steel.

Each tube 1 contains a cleaning spring 26, 30. In most of the tubes thecleaning spring 26 is mounted as shown in FIG. 5. This means that thesprings 26 belonging to two opposite tubes 1a, 1b, see also FIG. 4, areconnected to each other by means of two cables 27, 28 extending over thecable drums 13, 14 to form an endless loop. The cable drums 13, 14contain one groove 29 for each loop 26, 27, 28. The groove 29 issituated to be aligned with the corresponding pair of tubes 1a, 1b.

If a tube 1c, FIG. 4, does not have an opposite tube its cleaning spring30 is mounted as disclosed in FIG. 6. The two cables 31, 32 belonging tosaid spring 30 are wound on the cable drums 13, 14, extend via a groove33 in the adjacent cable drum into a tube 1a, in which they areinterconnected, by a coupling member 34, to form an endless loop. Thetube 1a also contains a cleaning spring 26 being part of a normalendless loop 26, 27, 28.

The member 17 for tightening the cables contains, as disclosed in FIG.7, a cylinder 35, fastened to a housing 36 for springs. The housing hasa cover 37. The cylinder 35 extends through the wall of the lowerhousing 12, and is fastened to said wall. Two piston rings 38 arearranged in grooves in the wall of the cylinder. The cylinder contains apiston 39 having a threaded upper portion 40 extending through thehousing 36. The threaded portion 40 supports an adjusting nut 41,fastened to a tube 42 extending through the cover 37. The top of thetube 42 is provided with an opening 59. A flat Teflon bearing 43 isplaced on the adjusting nut 41. The bearing 43 supports a disc 44fastened to a tube 45 which surrounds the tube 42 and extends throughthe cover 37. A stack of cup springs 46 are arranged on the disc 44,surrounding the tube 45. An opening 47 extends diametrically through thelower portion of the piston 39. Said piston 39 is connected to themovable frame 16 in the lower housing 12 by means of a split-pin, notshown, extending through said opening 47 and a corresponding opening inthe frame 16.

An electronic load relay, not shown, is connected to the electric cableof the motor 20, in series with the motor, which is an alternatingcurrent motor. Components, not shown, for the automatic operation areconnected to said relay.

The cleaning spring 26 has the double task of cleaning the tube wall 1and compensating for inaccuracies of the components actuating thetension of the cables 27, 28. It is difficult and expensive tomanufacture, in mass production, a cylindrical helical spring having theaccurate size required for use in the cleaning of tubes. The slightestoversize or undersize of the diameter results in a tendency of thespring to be jammed in the tube, or to loose its cleaning effect,respectively. It is an additional inconvenience of this type of springthat its diameter is reduced when its length is increased by traction.It is possible to make a spring from a comparatively thin wire, and tomake its diameter oversize, resulting in a resilient contact between thespring and the tube wall. However, pulling this spring through the tubeeasily results in an overload and in a permanent deformation of thespring. The cleaning spring 26 of the invention has been designedotherwise, resulting in several advantages.

The cleaning spring 26 of FIGS. 8 and 9 is a cylindrical helical spring.It contains 41/4 turns of a round steel wire having a diameter of 2.5mm. It has an extremely high pitch, for example 20 mm, and has an outerdiameter which is a few tenths of a millimeter smaller than the innerdiameter of the tube 1. The spring has shafts 48 extending from theperiphery of the spring with a great radius of curvature, for example 8mm. The shafts are bent into a substantially axial direction, and arealso bent a little outward in the radial direction. Axial holes 49 arebored at the extreme ends of the shafts. The two cables 27, 28 areinserted into said holes, and are fastened to the spring by brazing.

The cleaning springs 26 are pulled forward and back through the tubes1a, 1b by the cable loop 27, 28, which is driven by the upper cable drum13. The cable is placed in a V-shaped groove 29 in the cable drum, videFIG. 10. The groove 29 has an apex angle of 35°. The cable does nottouch the bottom of the groove, but is situated at such a depth in thegroove that a cross-section of the cable has normals 50 to the walls ofthe groove. The loop 26, 27, 28 is kept tight by means of the tighteningmembers 17. The cable 27, 28 is a multi-wire regular lay steel cablehaving a diameter of 1.5 mm. By having the shape of an endless loop thecable is secured against rotation and uncontrolled elongation when beingloaded. The tension in the cable is regulated so that the forceresulting from the friction in the V-groove 29 cannot exceed thepermitted tension in the spring 26 without sliding of the cable 27, 28in the groove 29. Whether the medium flowing through the tubes 1 haslubricating properties or not is a circumstance which affects the forceresulting from the friction in the V-groove very little. The lower cabledrum 14 is not driven, but is provided with V-grooves 29 correspondingto those of the upper cable drum 13. The majority of loops 27, 28 impartto the lower cable drum 14 a driving effect on single loops having alower tension, thus eliminating the tendency of skidding of said singleloops.

The cleaning effect of the spring 26 in the loop 26, 27, 28 is, asillustrated in FIG. 11, produced by the fact that the pulling force 51at both ends of the spring 26 acts in a point 52 which is eccentricallypositioned on the end surface of the cylinder defined by the spring 26.In a normal spring said pulling force acts in the center of the spring.The pulling force 51 had a direction practically parallel with thecenter line of the spring. This circumstance results, for all practicalpurposes, in a parallelogram of forces containing one component 53extending from said point 52 transverse to the spring. This component 53gives to the first turn of the spring two points of contact 54, 55 withthe tube wall, the first point 54 at half a turn, the second point 55 ata full turn. This first turn of the spring acts as a lever having twoarms and having its fulcrum in the point of contact 54. The balancingforces are the component 53 at the beginning of the turn, and thecounterforce from the tube wall in the point of contact 55 at the end ofthe full turn. Additional points of contact may be created at theintermediate turns of the spring, as repetitions of the first mentionedpoints of contact. In order to distribute the four points of contact 54,55 evenly round the tube wall, the final turn of the spring 26 onlycomprises 1/4 of a full turn, resulting in the shafts 48 beingdislocated 90° from each other. Consequently, the cleaning springobtains the double cleaning surface and the double cleaning effect. Thehigher the tension is in the loop 26, 27, 28, the smaller is thediameter of the spring 26, and the higher is the pressure of the springagainst the tube wall in the points of contact 54, 55, and,consequently, the better is the cleaning effect. The increased tensionin the loop 26, 27, 28 also increases the wedging effect of the V-groove29 on the cable, and consequently also the friction.

The flow velocity in the tubes is high, approximately 11/2 meter persecond. The velocity is highest in the center of the tube, and,theoretically, approaches zero in the layer close to the tube wall.Therefore, the design of the cleaning spring 26 as a cylindrical helicalspring having shafts 48 extending peripherally, and being fastened tothe cables without creating any loss of pressure, results in a cleaningmember producing a minimal loss of pressure, and leaving the centralopening of the spring free, to allow the passage of solid impuritiesaccompanying the flowing medium. The shafts 48 are prestressed by havingbeen bent outwardly, as mentioned above, with the result that saidshafts 48 and the cable 27, 28 stay close to the tube wall 1 even whentension is applied to the loop 26, 27, 28 and the component 51 in theparallelogram of forces referred to above tends to bend the shafts 48inwardly. This prestressing has the additional effect that the cleaningsprings 26 in a loop 26, 27, 28 having a lower tension exert a basiccleaning effect.

The wire of the cleaning spring may have any cross-sectional shape. Weprefer a round wire, i.e. a wire having a circular cross-section,because it results in several advantages. A round wire has a smallsurface of contact with the tube wall 1, and a large surface of contactwith the medium flowing in the tube. Therefore, the wire will have thesame temperature as the medium, thus eliminating the danger of aprecipitate covering the wire. The initial wear of the four points ofcontact 54,55 against the tube wall will rapidly result in widersurfaces of contact extending round the entire spring. The required wearis very small, because the difference in diameter between the spring 26and the tube 1 is small, and because the chord of the wire profile onwhich the wear takes place is short. The continued wear decreases as thelength of the chord increases. The wear affects the characteristics ofthe cleaning spring 26 only little, because the stresses determiningsaid characteristics are concentrated to the inner side of the springwire. The round wire profile, the large radius of curvature of the bentportion of the shafts, and the large pitch of the spring facilitate verymuch the insertion of the cleaning spring 26 into the tube 1.

Between cleaning operations the cleaning springs are positioned outsidethe tubes 1, haft the number of springs at each end of the heatexchanger. Placing the springs inside the tubes 1 would involve thedanger of galvanic corrosion, and would create an increased loss ofpressure. Placing the springs outside the tubes 1 facilitates thecleaning of the springs by the flowing medium being able to flush freelyaround the springs 26. Placing half the number of the springs at eachend of the heat exchanger also produces an additional advantage incertain heat exchangers, e.g. evaporators, in which a coating preferablyprecipitates in the evaporating portion of the tube 1. One cleaningspring 26 of each loop 26,27,28 will be pulled through a clean portionof a tube 1, while the other spring of said loop is being pulled througha coated portion of a tube. Halfway through the tubes the function ofthe springs will be reversed, resulting in a more even load of themotor, and in a better functioning of the automatic system.

Theoretically, all the 355 cleaning springs shall accompany each other,half in each direction. For various reasons a loop 27,28 may slide, thecleaning springs 26 of said loop coming behind the other springs, withthe risk of being positioned inside the tube 1. When moving in thereverse direction said springs will be ahead of the other springs, withthe risk of being pulled past the cable guides 23 to the cable drums 13,14 where they would be destroyed. The T-shaped rods 25 in the upperhousing 11 act, however, as stop rods. The cleaning spring 26 which isahead of the other springs is stopped when it reaches the slot 58 of thestop rod 25. The cables 27,28 of said cleaning spring now skid in thegroove 29 until the majority of the cleaning springs 26 have reached theslots 58. The braking force produced by said majority of springs givesan impulse to the electronic load relay mentioned above to stop themotor 20.

The stop rod 25 defines exactly the inactive position of the cleaningsprings 26. Therefore, it has been possible to locate said inactiveposition close to the place where an obstacle in the medium flow startscreating a measurable loss of pressure. This location of the inactiveposition makes it possible to build the two housings 11, 12 with a lowheight. Therefore, in the illustrated embodiment the housings 11,12 arecontained within the normal height of the two conical head chambersreferred to above.

As illustrated in FIG. 4, 10% of the tubes 1 have no opposite tuberequired for creating a normal loop 26,27,28. The problem has beensolved in the way illustrated by FIG. 6 as a result of the operation bymeans of cog wheels 18, i.e. as a result of the direct engagementbetween cog wheels 18 which are exactly alike, and as a result ofadjacent cable drums 13 having opposite directions of rotation and thesame velocity of rotation. The groove 33 pulls the cable, whereas thegroove 29 for the single tube 1c does not pull the cable. The connectingmember 34 is positioned close to the inner side of the cleaning spring26 in the tube 1a. Said connecting member 34, FIG. 13, consists of astraight piece of wire of the same diameter and material as the wireconstituting the cleaning spring 26, and of the same length as thespring 26. The connecting member 34 is fastened to the cables 31, 32 inthe same way as the cleaning spring 30. The single cleaning spring 30,FIG. 12, is wound to form 81/4 turns, so that its resilience shall beapproximately equal to that of two normal cleaning springs 26. The spacerequired for the extra turns of the spring 30 has been created by areduced pitch for all turns except the extreme turns. In other respects,all facts given for the normal spring 26 are true also for the spring30.

It is the object of the four tightening members 17 to move the frame 16,supporting the cable drums 14, downward, thus tightening the loops26,27,28 to such an extent that the V-grooves 29 in the cable drums 13of the upper housing 11 pull the cable. This is done by inserting antool into the opening 59 of the tube 49, and rotating the adjusting nut41 so as to move upward on the threaded portion 40, thus moving thepiston 39 downward. Simultaneously, the cup springs 46 are compressedbetween the nut 44 and the cover 37 to an extent proportional to thetension of the cables. Simultaneously, the tube 45 is being moved upwardabove the cover 37 by a distance corresponding to the compression of thestack of cup springs 46. Said distance represents the pressure of thepiston 39 on the frame 16. The distance can readily be measured by meansof a caliper rule, and the pressure is found by means of a table ofcalibration. The accuracy of the tightening member is 10 kilopond moreor less than the pressure obtained from the calibration. Therefore, thenumber, position and accuracy of the tightening members 17 permit a veryeven distribution of the tension in the loops 26, 27,28. The externaloperation of the tightening members 17 makes it possible to remove anybrittle deposited coating on the cleaning springs 26, viz. byalternatingly tightening and releasing the loops 26,27, 28, resulting inthe brittle coating being cracked and scaled off.

The motor 20, with its cog wheel gearbox, which drives the cable drums13, has a very low gear. Its output axle rotates with approximately 6r.p.m., imparting to the cleaning springs 26 a velocity of approximately20 mm per second. the coupling 21 is a high elasticity coupling,permitting 20° angular movement between the two halves upon a maximaltemporary load. The driving axle 22 is coupled to one of the twointermediate cable drums 13, thus minimizing the number of cog wheels 18connected in series, and the pressure between the cogs.

When the cleaning springs 26 have reached the stop rods 25, the load onthe motor 20 rapidly increases. An impulse to stop the motor 20 is nowcreated by an electronic load relay as disclosed in the Swedish Pat. No.8000672-9. The relay first measures the power fed to the motor 20, andsubsequently subtracts an amount which is proportional to the current tothe motor and to the internal loss of power. The compensation for theinternal loss can be regulated. The relay consists of a load detectorand a load converter. The load detector is adjustable for the highestpermitted load. It is provided with an output relay contact which stopsthe motor when the predetermined load limit has been exceeded. Thereaction time of the load detector is 0.1 second. As a consequence, anelectric contact governing the direction of rotation of the motor isautomatically switched over, and an adjustable time relay is started.When the predetermined time has lapsed, the time relay will start themotor. An impulse counter indicates the total number of cleaningoperations. The load limit is set so that a small number of cleaningsprings 26 are allowed to reach the stop rods 25, their cables 27,28sliding in the grooves 29, without the load limit being exceeded. When alarger number of springs 26 have reached the stops rods 25, and thepredetermined load limit has been exceeded, the motor 20 will be stoppedwithin the reaction time mentioned above. During this time the peripheryof the cable drums will rotate approximately 2 mm, but the cables 27will not slide in their grooves because of the soft braking of thesprings 26 produced by the elastic coupling 21, and because of the shortreaction time. The load converter is adjustable for an output signalwhich is proportional to the load of the motor 20. The output signal isconveyed to an indicating instrument and to a recorder.

The cleaning device is not accessible for inspection during operation.The indicating and recording members of the automatic system, theindicating tubes 45 of the tightening members 17, and the known membersof the heat exchanger for measuring the steam flow and the pressuredifferences, make it possible to draw conclusions on what adjustmentshave to be made from the outside of the device. Such adjustments may bechanging the frequency of the cleaning operations, changing the tensionof the cables to avoid sliding or to compensate for the wear of thecleaning springs or to increase the pressure of the springs against thetube wall 1.

The parts which are mainly consumed during operation are the cables27,28 and the cleaning springs 26. They last for approximately 50,000cleaning operations, for example one cleaning operation every 10 minutesfor one year.

OTHER EMBODIMENTS

Within the scope of the claims, the good results being maintained, thecleaning device may be varied in several realistic ways, as describedbelow.

In a heat exchanger having a large diameter, the bearings of the cabledrums may be situated within the periphery of the cluster of tubes 1. Ina heat exchanger having the tubes arranged in a complicated pattern, thecable drums may be placed in several levels. If the heat exchanger isdesigned with partitions in the head chambers, producing a repeated flowof the medium through the tubes, the cable drums 13, 14 may extendthrough said partitions. Alternatively, a separate housing for the cabledrums may be placed on top of the head chamber, and the cables 27,28,FIG. 14, may extend through openings 60 in the wall 56 separating thecable drum housing from the head chamber. The openings 60 are too smallfor the passage of the cleaning springs. A bushing 57 is fastened byscrew threads in each opening 60. Said bushing has a substantiallyconical opening 61 having a rounded surface so that the cable can slideon the bushing without wear. This structure has double functions, viz.that of the cable guide 23 and that of the stop rods 25. In addition,the opening 60,61 may guide the cable 27, 28 individually in alldirections, whereas the round rod 23 can only guide the cablescollectively and in one direction. This individual guiding of the cablesmakes it possible to guide the cables 27,28 also to a cluster of tubessituated in an asymmetric pattern relative to the positions of the cabledrums 13, 14. The method of guiding the cables by means of openings canbe used also in the main embodiment described above. In this case themembers 23,24,25,58 are replaced by horizontally situated rods in whichthe screws 57 have been fixed.

The V-shaped grooves 29 of the cable drums 13,14 may have a larger orsmaller apex angle than 35°, depending on to what extent the grooves aredesired to pull the cables. The V-shaped grooves 29 may be replaced bygrooves which do not pull the cables, for example grooves having a flatbottom and being wider than the diameter of the cable. The cable mayextend around the drum 13,14 more than the usual half turn. TheV-grooves 29 may be replaced by a shallow grooved surface having apattern fitting that of the wires of the cable.

The upper and the lower housings 11,12 with their components may changeplaces. The housings 11,12 may have different shapes, for example acylindrical shape. The shape may be such that the medium flows at anangle through the housing. The cog wheels 18 may be situated on the verydrums, i.e. between the bearings 15.

The tightening members 17 may be arranged to pull instead of push, orthey may be arranged to pull and push. The number of tightening membersmay be higher or lower than four. If the medium flows at an anglethrough the housing, the tightening members may be situated in the coverat the extreme end of the heat exchanger. The tightening members may bescrewed to the wall of the housing 12. Their adjusting and resilientcomponents 40-46 may be replaced by a piston or a membrane actuated bythe medium. In this case the tightening member 17 may have an internalposition, and the movable piston 39 may be replaced by a stationarypipe.

The cog wheel motor 20 may be replaced by a motor which is positionedinternally and is driven by the medium. In this case the movable axle 22is replaced by a stationary pipe. The members 18,20,21,22 driving thecable drums 13,14 may be divided into sections, each section having adriving motor. The members 18 connected in series to drive the cabledrums 13,14 may be replaced by a common axle and worm gears. Thefrictional driving grooves 29 in the cable drums 14 of the lower housing12 may be replaced by a synchronous transmission from the driving member20 for the cable drums of the upper housing 11.

The cleaning spring 26 may contain a higher or lower number of turnsthan the illustrated embodiment, which has 41/4 turns, preferably 11/4-7turns. The angular displacement of the shafts 48 may be different from90°. In tubes having a large diameter, said angular displacement may be0° or 180°, because the difference between the diameters of the tube 1and the cleaning spring 26 is proportionally smaller, and the size ofthe areas of contact 54,55 is proportionally larger. The eccentricposition of the point 52, in which the pulling force 51 acts upon theend surface of the cylindrical spring 26, may be varied from theperiphery to a point nearer the center. The position depends, i.a., uponthe desired pressure of the spring 26 on the tube wall relative to thetension of the cable and the permitted maximal load on the spring. Thedirection of the shaft 48 from the cleaning spring 26 to the cable 27,28may be varied. For example, the shaft 48 may extend in a radialdirection relative to the cylindrical spring 26, and may have a radialopening for the cable 27,28 in the point 52 where the pulling force 51acts upon the spring. The cable 27,28 may be fastened directly to thewire constituting the cylindrical portion 26 of the spring, by means ofa similar radial opening in said wire. If the tubes 1 consist of atender material, such as graphite, a scraping contact between the springand the tube wall is not desired. In this case, the point 52, in whichthe pulling force 51 acts upon the spring, may be positioned centrallyon the end surface of the cylindrical spring 26. Said central positionmakes it possible to adjust exactly the depth of cleaning, withoutscraping, viz. by the combination consisting of the external adjustmentof the tightening members 17, the accuracy of said adjustment, the loadconverter of the automatic system, and the reduction of the diameter ofthe spring when being elongated. The turns of the spring 26 at itsextreme ends may have a somewhat conical shape, thus making it stillmore easy to insert the cleaning spring 26 into the tube 1. The spring26 may be wound with a right-hand or left-hand pitch. The wire of thecleaning spring 26 may consist of another suitable material, such asstainless steel, a non-ferrous metal, titanium, or a composite materialof plastic and fibers. The wire may have a square cross-sectional shape.Its surface may be treated to reduce the adhesion of the scraped-offcoating, for exemple electro-polished or Teflon-coated.

Under difficult cleaning conditions it may be to advantage that thecable loop 27,28 contains only one cleaning spring 26, instead of two.One of the two springs has been replaced by a coupling member 34, andthe cable drums 13,14 contain the double number of grooves 29. Insteadof being joined to the spring 26 and to the coupling member 34 bybrazing, it may be hooked or screwed or pressed fast to said spring andsaid member.

The cable 27,28 may consist of another material, such as stainlesssteel, a non-ferrous metal, titanium, or a composite of plastic andfibers. The cable may be wound in another pattern. One of the cables27,28 may be wound with a right-hand pitch, the other with a left-handpitch, to counteract the rotation of the cable.

The load detector may be supplemented with a known time-meter orposition-meter designed to stop the motor 20 just before it would havebeen stopped by the load detector. This device reduces the wear of thecables 27 and the coupling 21 occurring when the cleaning springs 26 arestopped by the stop rod 25. A programmer shifts the device between saidtwo stopping methods, so that, say, five cleaning operations with anearly stop before the stop rod 25 are followed by a cleaning operationwith an ordinary stop by means of the stop rod 25. Another method to thesame effect is to use a two-speed cog-wheel gear motor 20. The impulsefor changing the speed of the motor is received either from the loadconverter, viz. when the signal from said load converter becomes weakeras a result of the springs 26 leaving the tubes 1, or from thetime-meter or the position-meter. The last-named method permits a higherspeed of the cleaning springs in the tubes. Finally, the load detectormay in a known way base its determination of the load upon one or moreother electrical characteristics of the motor 20, than those mentionedin the Swedish patent referred to above, e.g. the current or the powerof the motor, or the phase difference between the voltage and thecurrent of the motor.

I claim:
 1. A device for internal cleaning during operation, of thetubes of a heat exchanger containing a plurality of substantiallystraight tubes having both ends fastened to tube sheets; and headchambers outside the tube sheets for the medium flowing through thetubes comprising cleaning members in each of the tubes, driving meanscomprising cable drums, cables in contact with said drums to pull thecleaning members through the tubes, each end of each cleaning memberbeing attached to a cable end; and wherein each of the cleaning memberscomprises a substantially cylindrical helical spring having an axisextending along a tube axis, the spring being open centrally to permitstraight and free flow of said medium, the spring having an externaldiameter which, in the unloaded condition of the spring, is slightlysmaller than the internal diameter of the tube in which the spring islocated, and the cable attachment point to at least one of the springends is located offset from the spring axis.
 2. A device according toclaim 1, wherein both the cable attachment points to the spring ends arelocated offset from the spring axis.
 3. A device according to claim 1wherein each spring comprises a whole number of turns plus a fraction ofa turn, as measured from the points in which a cable end is attached toeach spring.
 4. A device according to claim 2 wherein each springcomprises a whole number of turns plus a fraction of a turn, as measuredfrom the points in which a cable end is attached to each spring.
 5. Adevice according to claim 3 wherein said fraction is about 1/4 of aturn.
 6. A device according to claim 4 wherein said fraction is about1/4 of a turn.
 7. A device according to claim 3 wherein straight endportions extend from said fraction of a turn, said end portions lying inaxial planes of the spring and being directed away from the spring coil.8. A device according to claim 5 wherein straight end portions extendfrom said fraction of a turn, said end portions lying in axial planes ofthe spring and being directed away from the spring coil.
 9. A deviceaccording to claim 7 wherein the straight end portions slightly divergefrom the spring axis, in direction away from the spring coil.
 10. Adevice according to claim 8 wherein the straight end portions slightlydiverge from the spring axis, in direction away from the spring coil.11. A device according to claim 7 wherein the ends of the spring haveaxial blind holes for receiving the cable ends.
 12. A device accordingto claim 9 wherein the ends of the spring have axial blind holes forreceiving the cable ends.
 13. A device according to claim 1 whereinmeans for tightening the cables are provided to maintain the springtensioned so as to engage the tube wall.
 14. A device according to claim2 wherein means for tightening the cables are provided to maintain thespring tensioned so as to engage the tube wall.
 15. A device accordingto claim 3 wherein means for tightening the cables are provided tomaintain the spring tensioned so as to engage the tube wall.
 16. Adevice according to claim 3 characterized in that said fraction is about3/4 of a turn.